lib: change concatenated string to template

PR-URL: #16930
Reviewed-By: Tobias Nießen <tniessen@tnie.de>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Franziska Hinkelmann <franziska.hinkelmann@gmail.com>

lib/dns.js

@@ -46,7 +46,7 @@ function errnoException(err, syscall, hostname) {
   }
   var ex = null;
   if (typeof err === 'string') {  // c-ares error code.
-    const errHost = hostname ? ' ' + hostname : '';
+    const errHost = hostname ? ` ${hostname}` : '';
     ex = new Error(`${syscall} ${err}${errHost}`);
     ex.code = err;
     ex.errno = err;